Electrical circuits using multi-gap cold cathode gas filled tubes



United States Patent ELECTRICAL CIRCUITS USING MULTI-GAP COLD CATHODE GAS FILLED TUBES Thomas Meirion Jackson and Ian Hugh Fraser, London, England, assignors to International Standard Electric Corporation, New York, N. Y.

Application October 20, 1954, Serial No. 463,450

Claims priority, application Great Britain November 12, 1953 5 Claims. (Cl. SIS-84.6)

The present invention relates to electrical circuits employing multi-gap cold-cathode gas-filled discharge tubes of the type which have storage gaps and transfer gaps. Tubes of this type are described and claimed in United States patent specification No. 2,553,585 (G. H. Hough), for Electric Discharge Tubes, issued May 22, 1951.

It has been found with tubes of this type that when the tube is allowed to remain with the discharge on one storage cathode for a relatively long time there is a risk that the discharge will fail to advance to the next storage cathode in response to the next received pulse, which pulse should cause this advance.

The object of the present invention is to provide an electrical circuit for a multi-cathode cold-cathode gasfilled discharge tube of the type having storage gaps and transfer gaps in which the disadvantage just mentioned is overcome.

According to the present invention there is provided an 0 cathode supply circuit when a transfer gap is discharging.

According to the present invention there is further provided an electrical circuit which comprises a multi-cathode cold-cathode gas-filled discharge tube of the type having alternate storage cathodes and transfer cathodes which with a common anode define an array of alternate storage gaps and transfer gaps, a source of current associated with all of said gaps which is substantially non-effective when a storage gap alone is discharging, and circuit means responsive to initiation of a discharge in a transfer gap to render said current source effective, whereby currentflows from said current source as well as from the anode-cathode supply circuit when a transfer gap is discharging.

Thus it will be seen that the effect of the provision of the current source referred to in the preceding paragraphs is to ensure that the current which flows in a transfer gap is increased with respect to that which flows in a storage gap.

The invention will now be described with reference to the accompanying drawings, in which Figs. 1 and 2 resepectively show two embodiments of the invention.

The circuits described herein may be used for example with the G/241E tube as sold under the Registered Trade Mark Nomotron of International Standard Electric Corporation. These tubes are of the type which is covered by and fully described in the above mentioned United States patent. Such tubes have alternate storage cathodes and transfer cathodes, of which all transfer cathodes are internally commoned. These tubes also have additional electrodes known as control plates whose function is to control the area of the cathode glow and to screen the discharge gaps from external influences. These 2,749,479 Fatented June 5, 1956 control plates and, in fact the other electrodes are arranged in the manner shown in Figs. 5 to 9 of the abovementioned United States patent.

The present invention is also applicable to circuits using other tubes of generally similar type, for instance, tubes without the control plates.

Turning now to Fig. 1, the tube MCT contains alternate storage cathodes such as SC, each of which may be formed in the manner described in the above-mentioned U. S. patent, and transfer cathodes such as TC, each of which may be formed in the manner described in the said U. S. patent. The control plates are arranged, as already stated in the manner described in the above U. S. patent. However, to simplify the circuits they are represented schematically by the single electrode C. Each of the storage cathode such as SC is connected to earth via a resistorcapacitor circuit such as R1C1, and the anode .A is connected to a high positive voltage via resistors R2 and R3. The transfer cathodes such as TC are commoned, i. e. connected together, and are connected via resistor R4 and rectifier MRl'to a point on a potential divider formed by resistors R6, R7. R6 and R7 are such that the normal potential on the transfer cathodes is of the order of 70 volts. Suitable values for these resistors in one embodiment was found to be 56,000 ohms for R6 and 15,000 ohms for R7. The capacitor C1 stabilises the potential at the junction of resistors R6 and R7, and a suitable valve therefore is 4 f. The rectifier MR1 ensures that although the transfer cathode potential can fall below 70 volts it cannot rise above it. Negative stepping pulses for the tube are applied at terminal P via capacitor C2, which can have a value of 0.01 pfJ The connection to the transfer cathodes is via resistor R4, which in said embodiment had a value of 8,200 ohms and which'redu ces the maximum voltage present on the transfer cathodes. This measure is called for because otherwise there is some risk of a breakdown between a transfer cathode and the control plates C. Resistor R5, which may have a value of l megohm, ensures that current flows in MR1, which facilitates the action of this rectifier already described.

The control plates, which as already mentioned are represented schematically by C, are connected via a current limiting resistor R8 to a point on a bleeder formed by resistors R9 and R10. These resistors in the mentioned embodiment were respectively of 100,000 ohms, 56,000 ohms and 27,000 ohms values.

The injunction of the anode load resistors R2 and R3 is connected via a rectifier MR2 to a stabilised positive potential source of 280 volts. Resistors R2 and R3 were of 12,000 ohms'an'd 27,000 ohms respectively in said embodiment, so that in the normal condition with the discharge on a storage cathode the tube passes a current of about 2.5 mA. Under these conditions the junction of resistors R2 and R3 is at a voltage close to 280 volts, so MR2 is non-conductive. Clearly if the tube used is intended to pass a different current, or if different supply voltages are employed, resistors R2 and R3 would need to be altered accordingly. In any case, the normal condition is with rectifier MR2 just non-conductive.

When a negative pulse is applied to the transfer cathode TC via terminal P, C2 and R4, the gap including the transfer cathode next to the discharging storage cathode in the desired direction of travel fires. This occurs by the mechanism described in the above-mentioned patent specification No. 2,553,585. When this happens, an increased current flows in the anode circuit of tube MCT, so that the voltage at the junction of resistors R2 and R3 falls below 280 volts, with the result that rectifier MR2 becomes conductive. Hence the supply during this condition comes from both the normal anode voltage supply and the additional supply so that a heavier current can pass between the anode and a transfer cathode than between the anode and a storage cathode. As a further consequence of the increased current flowing in the anode circuit of tube MCT, the increased voltage drop across the resistors R2, R3, R1 reduces the voltage across the discharging storage gap to a point below the discharge-maintaining level, so that this gap is extinguished.

Under normal operating conditions, i. e. in the absence of the additional supply source, a transfer gap when fully discharging passes a somewhat heavier current than does a storage gap. This increased current facilitates the extinction of the previously firing storage gap. By the provision of the additional supply, the current which flows when a transfer gap discharges is increased further. This further increase has the effect of making the extinction of the storage gap just mentioned more certain. Then the risk of the discharge failing to stop is substantially eliminated.

At the end of the pulse, the transfer cathode voltage returns to its normal value at which the discharge cannot maintain, so the discharge is extinguished.

The next adjacent storage cathode is at earth potential, and the immediately-preceding one is at a positive potential due to the Re circuit such as Rl-Cl, so the neXt adjacent storage gap fires. This leaves the circuit in its original condition except that the discharge has been moved one step along.

The modification shown in Fig. 2 is a simpler circuit than that shown in Fig. l and does not need a stabilised voltage supply. In this modified circuit most of the component values are the same as in Fig. 1. However, connected across resistor R3 there is a capacitor C3, which can be 0.2 microfarad. This capacitor becomes charged to the voltage across resistor R3 between pulses. During the interval between pulses the value of the voltage at the junction of resistors R2 and R3, which determines the voltage to which capacitor C3 charges, is intermediate the value of the supply voltage and the value of the voltage on the anode of the tube. As long as this state persists, C3 will remain charged to the voltage across R3. However, when a negative pulse is applied to terminal P, a discharge is initiated on the transfer cathode in advance of the discharging storage cathode. This increases the current flowing through resistors R2 and R3 in series, so that the voltage at the junction of R2 and R3 moves in a negative direction. Since the voltage to which the lower plate of capacitor C3 was charged before this increased current fiow commenced was positive with respect to the new voltage at the junction of resistors R2 and R3, C3 commences to discharge through the anode circuit of the tube MCTA. The discharge circuit of C3 therefore supplies current, i. e. C3, by virtue of its charged condition acts as an additional current source which only becomes effective when a transfer gap discharge is initiated. This increased current acts in the manner already described during the discharge of the transfer gap. The value of C3 should be so chosen that it does not discharge appreciably for the duration of an input pulse. This ensures that the inter-pulse period will allow time for C3 to recharge to its pre-pulse level.

While the principles of the invention have been described. above. in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What we claim is:

1. An electrical circuit which comprises a multi-gap cold-cathode gas-filled discharge tube of the type having storage gaps and transfer gaps, a source of current associated with all of said gaps which is substantially noneffective when a storage gap alone is discharging, and circuit means responsive to the initiation of a discharge in a transfer gap to render said current source etfective, whereby current flows from said current source as well as from the anode-cathode supply circuit when a transfer gap is discharging.

2. An electrical circuit which comprises a multi-cathode cold-cathode gas-filled discharge tube of the type having alternate storage cathodes and transfer cathodes which with a common anode define an array of alternate storage gaps and transfer gaps, an anode-cathode supply circuit, a source of current associated with all of said gaps which is substantially non-effective when a storage gap alone is discharging, and circuit means responsive to initiation of a discharge in a transfer gap to render said current source effective, whereby current flows from said current source as well as from the anode-cathode supply circuit when a transfer gap is discharging.

3. An electrical circuit as claimed in claim 2, in which said current source is a supply whose voltage is less than the anode-cathode supply voltage, and in which said circuit means comprises an anode load impedance, 3. rectifier connected to said current source and so poled as to be in the direction of easy conductivity for current flowing away from said current source, and which rectifier is in a connection from said current source to a point in said anode load impedance such that when a storage gap alone is discharging said rectifier is in its non-conducting condition and when a discharge is initiated in a transfer gap said rectifier conducts.

4. An electrical circuit as claimed in claim 2, in which said current supply is formed by a capacitor connected in parallel with a part of said anode load impedance and which is normally charged to a voltage equal to the voltage drop across said part of the anode load when a storage gap alone is discharging, and in which said circuit means is formed by said anode load impedance which comprises the part across which said capacitor is connected and a further part between said capacitor and said tube, the capacitor commencing to discharge when a transfer gap is fired.

5. An electrical circuit as claimed in claim 3, and in which said anode load is formed by two resistors connected in series.

References Cited in the file of this patent UNITED STATES PATENTS 2,553,585 Hough May 22, 1951 

